Distinguish between MTU and MSS.

Have the application set the maximum size of a UTCP packet (= MTU), and from
that derive the maximum size of the payload of a UTCP packet (= MSS).

diff --git a/test.c b/test.c
index e04e17bec2e6e7cfb5154bc59aaa9e4fcb4142f6..300ce51e4d3a0cb8f636038a7ca8b766f4c7e39c 100644 (file)
--- a/test.c
+++ b/test.c
@@ -159,7 +159,7 @@ static void set_mtu(struct utcp *u, int s) {
 
        debug("Using MTU %lu\n", mtu);
 
-       utcp_set_mtu(u, mtu ? mtu - 48 : 1300);
+       utcp_set_mtu(u, mtu ? mtu - 28 : 1300);
 }
 
 int main(int argc, char *argv[]) {

diff --git a/utcp.c b/utcp.c
index ac598ddae28667fd9a40c28ace29255b7dd22f66..72bb41d021f003e49897d24b92bcfda0456846cb 100644 (file)
--- a/utcp.c
+++ b/utcp.c
@@ -401,7 +401,7 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
        c->snd.una = c->snd.iss;
        c->snd.nxt = c->snd.iss + 1;
        c->snd.last = c->snd.nxt;
-       c->snd.cwnd = (utcp->mtu > 2190 ? 2 : utcp->mtu > 1095 ? 3 : 4) * utcp->mtu;
+       c->snd.cwnd = (utcp->mss > 2190 ? 2 : utcp->mss > 1095 ? 3 : 4) * utcp->mss;
        c->snd.ssthresh = ~0;
        debug_cwnd(c);
        c->utcp = utcp;
@@ -535,8 +535,8 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
        } else if(cwndleft < left) {
                left = cwndleft;
 
-               if(!sendatleastone || cwndleft > c->utcp->mtu) {
-                       left -= left % c->utcp->mtu;
+               if(!sendatleastone || cwndleft > c->utcp->mss) {
+                       left -= left % c->utcp->mss;
                }
        }
 
@@ -551,7 +551,7 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
                uint8_t data[];
        } *pkt;
 
-       pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
+       pkt = malloc(c->utcp->mtu);
 
        if(!pkt) {
                return;
@@ -565,7 +565,7 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
        pkt->hdr.aux = 0;
 
        do {
-               uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
+               uint32_t seglen = left > c->utcp->mss ? c->utcp->mss : left;
                pkt->hdr.seq = c->snd.nxt;
 
                buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
@@ -710,7 +710,7 @@ static void fast_retransmit(struct utcp_connection *c) {
                uint8_t data[];
        } *pkt;
 
-       pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
+       pkt = malloc(c->utcp->mtu);
 
        if(!pkt) {
                return;
@@ -731,7 +731,7 @@ static void fast_retransmit(struct utcp_connection *c) {
                pkt->hdr.seq = c->snd.una;
                pkt->hdr.ack = c->rcv.nxt;
                pkt->hdr.ctl = ACK;
-               uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mtu);
+               uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mss);
 
                if(fin_wanted(c, c->snd.una + len)) {
                        len--;
@@ -764,7 +764,7 @@ static void retransmit(struct utcp_connection *c) {
                uint8_t data[];
        } *pkt;
 
-       pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
+       pkt = malloc(c->utcp->mtu);
 
        if(!pkt) {
                return;
@@ -808,7 +808,7 @@ static void retransmit(struct utcp_connection *c) {
                pkt->hdr.seq = c->snd.una;
                pkt->hdr.ack = c->rcv.nxt;
                pkt->hdr.ctl = ACK;
-               uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mtu);
+               uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mss);
 
                if(fin_wanted(c, c->snd.una + len)) {
                        len--;
@@ -817,8 +817,8 @@ static void retransmit(struct utcp_connection *c) {
 
                // RFC 5681 slow start after timeout
                uint32_t flightsize = seqdiff(c->snd.nxt, c->snd.una);
-               c->snd.ssthresh = max(flightsize / 2, utcp->mtu * 2); // eq. 4
-               c->snd.cwnd = utcp->mtu;
+               c->snd.ssthresh = max(flightsize / 2, utcp->mss * 2); // eq. 4
+               c->snd.cwnd = utcp->mss;
                debug_cwnd(c);
 
                buffer_copy(&c->sndbuf, pkt->data, 0, len);
@@ -1425,9 +1425,9 @@ synack:
 
                // Increase the congestion window according to RFC 5681
                if(c->snd.cwnd < c->snd.ssthresh) {
-                       c->snd.cwnd += min(advanced, utcp->mtu); // eq. 2
+                       c->snd.cwnd += min(advanced, utcp->mss); // eq. 2
                } else {
-                       c->snd.cwnd += max(1, (utcp->mtu * utcp->mtu) / c->snd.cwnd); // eq. 3
+                       c->snd.cwnd += max(1, (utcp->mss * utcp->mss) / c->snd.cwnd); // eq. 3
                }
 
                if(c->snd.cwnd > c->sndbuf.maxsize) {
@@ -1466,8 +1466,8 @@ synack:
                                // RFC 5681 fast recovery
                                debug(c, "fast recovery started\n", c->dupack);
                                uint32_t flightsize = seqdiff(c->snd.nxt, c->snd.una);
-                               c->snd.ssthresh = max(flightsize / 2, utcp->mtu * 2); // eq. 4
-                               c->snd.cwnd = min(c->snd.ssthresh + 3 * utcp->mtu, c->sndbuf.maxsize);
+                               c->snd.ssthresh = max(flightsize / 2, utcp->mss * 2); // eq. 4
+                               c->snd.cwnd = min(c->snd.ssthresh + 3 * utcp->mss, c->sndbuf.maxsize);
 
                                if(c->snd.cwnd > c->sndbuf.maxsize) {
                                        c->snd.cwnd = c->sndbuf.maxsize;
@@ -1477,7 +1477,7 @@ synack:
 
                                fast_retransmit(c);
                        } else if(c->dupack > 3) {
-                               c->snd.cwnd += utcp->mtu;
+                               c->snd.cwnd += utcp->mss;
 
                                if(c->snd.cwnd > c->sndbuf.maxsize) {
                                        c->snd.cwnd = c->sndbuf.maxsize;
@@ -1979,6 +1979,7 @@ struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_
        utcp->send = send;
        utcp->priv = priv;
        utcp->mtu = DEFAULT_MTU;
+       utcp->mss = DEFAULT_MTU - sizeof(struct hdr);
        utcp->timeout = DEFAULT_USER_TIMEOUT; // sec
        utcp->rto = START_RTO; // usec
 
@@ -2020,6 +2021,7 @@ void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
        // TODO: handle overhead of the header
        if(utcp) {
                utcp->mtu = mtu;
+               utcp->mss = mtu - sizeof(struct hdr);
        }
 }
 

diff --git a/utcp_priv.h b/utcp_priv.h
index 5ed0344a45fce589963253eafe5ec11bbcdfc937..de942a8968ae61ef27592126244ad935dcfe5475 100644 (file)
--- a/utcp_priv.h
+++ b/utcp_priv.h
@@ -171,7 +171,8 @@ struct utcp {
 
        // Global socket options
 
-       uint16_t mtu;
+       uint16_t mtu; // The maximum size of a UTCP packet, including headers.
+       uint16_t mss; // The maximum size of the payload of a UTCP packet.
        int timeout; // sec
 
        // RTT variables